Most NFTs are meant to function like a certificate of ownership to some external thing. The proof of ownership is decentralized, even if the thing itself is not. And like any such certificate, it's only useful insofar as whoever actually controls the thing agrees your certificate is legit (or can be compelled to recognize it as such).
If there's an NFT that says you're the owner of a fancy bottle of wine stored in some wine vault somewhere, you'll never sniff that wine unless the proprietor of the vault agrees you own it and is willing to surrender it to you. If an NFT says you own 5 bushels of lettuce on a truck headed out of Walla Walla, you'll never see those bushels unless the trucking company agrees you own the lettuce and is willing to deliver it to your care. If an NFT says you own a hilarious GIF hosted somewhere on the Internet, you'll never gaze upon it unless that hosting service agrees to serve it to you.
If I scribbled on the back of a napkin that I was transferring my immortal soul to you, could you redeem that napkin for my soul? Would it make a difference if I put the deed on the blockchain? I would say the only differences between the napkin and the blockchain are 1) anyone can see it on the blockchain; 2) on the blockchain the deed can't be tampered with later; 3) the blockchain can include some programmatic constraints/triggers on the transaction (eg to make sure I can only sell my soul once, I can only sell my own soul, I'm now flagged as doomed to wander the earth in eternal torment, etc).
